The effect of AlF3 on the decomposition of CF3OCF3 and CF3CF2OCF2CF3 is investigated using ab initio theory. Previous work by Pancansky et al. [Pacansky, J.; Waltman, R. J. J Fluorine Chem. 1997, 83, 41] showed that AlF3 significantly reduces the activation energy of the decomposition of CF3OCF3 due to the strong electrostatic interaction between the aluminum trifluoride and the reactant. In this work, a new transition-state structure and reaction mechanism have been identified for the decomposition of CF3OCF3 in the presence of AlF3. This new mechanism shows that AlF3 functions by accepting a fluorine atom from one carbon and simultaneously donating a fluorine atom to the other carbon. We show that the same pathway is obtained independently of the level of theory. The reaction rate, generated via statistical mechanics and transition-state theory, is 2-3 orders of magnitude higher for the new transition state when compared to that of the old one. The study was also performed for CF3CF2OCF2CF3 in order to ascertain the effect of chain length on the reaction mechanism and rate. We find that an analogous transition state, with lower activation energy, provides the lowest-energy path for decomposition of the longer chain.